Automatic pump control system

ABSTRACT

A control system for plural motor-driven hydraulic pumps. The pumps are arranged in pairs, each pair connected in a hydraulic actuating circuit individual to that pair and each circuit including a piston-type actuator to be advanced and retracted by fluid under pressure developed from the paired pumps of that circuit. A single prime mover drives the pumps of both pairs, and each circuit has a pressure-responsive control valve which provides for unloading of one pump of the other circuit when the pressure in one circuit increases to a predetermined value at which, in the absence of such unloading, the input horsepower requirement has risen toward a value which would stall the prime mover.

United States Patent Ratliff et al.

1 1 AUTOMATIC PUMP CONTROL SYSTEM Inventors: Frank W. Ratliff, Oak Forrest Estate; James R. McBurnett, Corinth, both of Miss.

Tyrone Hydraulics, Inc., Corinth, Mass.

Filed: Mar. 20, 1974 Appl. No.: 452,713

Assignee:

US. Cl 60/421, 60/426, 60/468, 60/486, 91/412 Int. Cl. FlSb 18/00 Field of Search 91/412; 60/420, 421, 426, 60/428, 430, 486, 468

References Cited UNITED STATES PATENTS Adams et a1. 60/426 3,535,877 10/1970 Becker et al 91/412 X Primary E.\'aminerEdgar W. Geoghegan Attorney, Agent, or F irm--Synnestvedt & 'Lechner [57] ABSTRACT A control system for plural motor-driven hydraulic pumps. The pumps are arranged in pairs, each pair connected in a hydraulic actuating circuit individual to that pair and each circuit including a piston-type actuator to be advanced and retracted by fluid under pressure developed from the paired pumps of that circuit. A single prime mover drives the pumps of both pairs, and each circuit has a pressure-responsive control valve which provides for unloading of one pump of the other circuit when the pressure in one circuit increases to a predetermined value at which, in the absence of such unloading, the input horsepower requirement has risen toward a value which would stall the prime mover.

PATENTEDHAR 4% 3,868,821

sum 2 9f 2 AUTOMATIC PUMP CONTROL SYSTEM BACKGROUND OF THE INVENTION The invention is broadly useful in the field of hydraulically actuated equipment, being applicable, for example, to backhoes which include at least two cylinders containing actuating pistons. It is known in such apparatus to provide two separate circuits each of which includes: a cylinder and piston; two pumps; a manual control valve affording control of the position of the piston; and pressure-responsive valve means for unloading one of the circuit pumps in response to high pressure existing in that circuit. In a backhoe, as will be understood the piston of one circuit may control the position of the stick, as during the crowding operation, and the other piston may rotate the bucket in the customary curling and dumping operations. Tandem pumps may also be used to supply two speed track drive, with either manual or automatic upshift and down-shift. The invention is described in what follows, as applied to control of stick and bucket.

In such systems it is usual that a single prime mover serves both to move the backhoe and to drive several pumps, preferably four, which supply the pressurized fluid for the pistons of the two circuits. The pumps are arranged in pairs, and each pair forms part of one of the two hydraulic circuits. In this arrangement the power required of the prime mover, for pumping purposes, is the sum of the power required at the four pumps. The input horsepower requirement at the prime mover is a function of the flow rate of the pumps, the pressure existing in each circuit, and the overall efficiency of the pumping system.

Generally the pumps are driven at constant speed, and hence the flow rate (gals/min.) is very nearly constant. It follows that the input horsepower required of the prime mover, which is coupled to drive all the pumps, rises linearly with the pressures in the circuits, that is, with the pressures developed in the cylinderpiston actuators. When the pressure in either or both cylinders rises substantially, as frequently occurs during a digging operation, the required input horsepower advances toward, and may exceed, the maximum available horsepower. If the maximum is exceeded, the diesel or gasoline motor used as a prime mover will stall.

The prior art includes various arrangements intended to prevent such stalling by unloading one or more pumps, if the pressure in the cylinder circuits approaches a predetermined maximum value, and the present invention provides a novel and particularly advantageous unloading arrangement.

SUMMARY OF THE INVENTION It is the general objective of this invention to provide what can be termed a cross-over unloading arrangement in which, if the piston in a first actuating circuit is not requiring substantial horsepower since it is operating under a lower pressure condition, and if the piston in the second circuit encounters a high load condition, the resultant elevated pressure in said second circuit is utilized to unload a pump in one of the circuits. Specifically, the invention contemplates cross-over unloading of the pump which is requiring lesser horsepower, as well as other desirable unloading sequences to be referred to later in this description. Since the power required of the prime mover, for pumping purposes, is the sum of the power consumed at all the pumps, controlled unloading of the pumps is provided in order that power will be available where required, and to prevent stalling.

In the achievement of these advantages, the invention utilizes particularly designed. pilot-operated unloading valves, in novel cross-over arrangement, and it is an object to provide these valves in such arrangement.

It is a further object to devise double hydraulic, piston-actuating circuits having cross-over unloading relief such that four, three, or even two pumps may be pumping, in accordance with the pressures existing in each of the two hydraulic circuits.

With particular reference to backhoes, it is a feature of the invention that, when an excess power requirement develops at the stick cylinder for example, as may occur during crowding, one of the two pumps which has been controlling curl is unloaded, increasing the power available for the stick cylinder. Should a similar overload exist at the bucket cylinder, it is sensed at the pressure-responsive control valve in the stick circuit, moving the stick circuit control valve to a position in which one of the pumps of the stick circuit is also unloaded.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a schematic illustration of apparatus including a pair of hydraulic circuits for actuating portions of a hydraulic implement, such as a backhoe, said apparatus embodying the unloading arrangement characteris tic of this invention;

FIG. 2 is a partly sectional and partly schematic illustration of a pilot-operated pump-unloading valve of the kind included in each of the actuating circuits;

FIG. 3 is a view similar to FIG. 2, and illustrating the valve under a different condition of operation; and

FIG. 4 is an isometric view of a poppet valve member used in the pilot mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With initial reference to FIG. 1, the hydraulic system of the invention comprises two similar circuits 10 and 11. Each circuit includes an element to be actuated by output of a pair of pumps, and a manually operable control valve for directing pressurized fluid from the pumps in such manner as to move the element in either of two senses. The circuits further include unloading valves which are designed, in the illustrated embodiment, to respond to pressures communicated through cross-over connections so arranged that pressure above a predetermined relief point in circuit 10 will unload a pump in circuit 11, and vice versa. These similar circuits will now be described in greater detail with refer ence to circuit 10. Corresponding parts in circuit 11, which functions in the same manner as circuit 10, bear the same numerals with the subscript a.

Cylinder 12 of circuit 10 houses a piston 13 which, when the apparatus is embodied :in a backhoe, should be understood as being connected to advance or retract an operating element, e.g., a crowd stick (not shown), during digging and dumping operations. Piston 13a in circuit 11 would then be connected to control a bucket (not shown). A manually operable valve of known type is represented conventionally at 14 in FIG. 1, and it will be understood without detailed description that this valve can be moved, by handle 15, from the illustrated center position to righthand or lefthand positions in which, respectively, the piston 13 is advanced or retracted with respect to the cylinder. In the center position there is no actuation of the piston 13 since the hydraulic fluid arriving through the pressure line 16 is bypassed directly to the fluid reservoir indicated at 17.

As illustrated, the pump means of each circuit comprises tandem pump means, preferably a pair of gear pumps, shown at 18 and 19in circuit 10. As shown, the pumps are connected to be driven by a single prime mover 20 (see linkage 20 and 20") which may be the diesel or gasoline engine of a backhoe. The power required of the prime mover 20 for pumping purposes is, of course, the sum of the power required at the four pumps. Assuming low pressures prevail in both circuits 10 and 11, the fluid delivered to main pressure line 16 will be the composite flow derived from pump 18 and from pump 19, the latter through a connection 21 containing a check valve 22. The pressure of this composite flow is designated P (P in circuit 11), and exists downstream of the pair of pumps 18 and 19. This pressure is of course affected by the load encountered at piston 13, as will be understood by those skilled in this art.

The usual maximum pressure unloader appears at 23. This unloader is of the known bleed orifice type (see orifice 24), and is spring-adjusted to terminate all flow to the valve 14 and cylinder 12 in the event that P, rises to a maximum value. This value is greater than, and is to be distinguished from, the relief pressure values which result in unloading, and consequent reduction of the pumping capacity.

In particular accordance with the present invention, each circuit includes a pressure-operated unloading valve 25, with poppet-type pilot actuator 26, and a brief discussion of the nature and operation of these valves follows. This brief discussion is with reference to the schematic showings of FIG. 1, and will be followed by more detailed consideration of the construction of the valves 25 and 26, referring to FIGS. 24. In FIG. 1 the pilot parts and connections, which control valve 25, have been shown in broken lines.

In the lefthand position of valve 25, as it is shown in FIG. 1, the flow of fluid from pump 19 is through conduit 21 and check valve 22, and this flow is added to the flow derived from pump 18. The composite flow is available in pressure line 16 to control piston 13. Spring S biases the spool type valve 25 toward the illustrated lefthand position (as seen in FIG. 1) which it occupies during normal low pressure operation. It will be understood that valve 25a operates in similar fashion to provide flow from both of pumps 18a and 19a in circuit 11.

Consideration is now given to the novel unloading arrangements provided by this invention, it being assumed for exemplary purposes that the pump operating in the circuit at lower pressure is to be unloaded first, should an overload occur. Should a high pressure condition arise in circuit 11, due to excessive load encountered at piston 13a, this pressure is communicated through cross-over passage 27a which extends from one side of poppet valve 26 of circuit 10 and maintains it in communication with prpessure feed line 16a of circuit 11. It should be noted that the other cross-over passage 27 interconnects circuit 10 and one side of poppet valve 26a of circuit 11.

Valve 25 can be moved to its righthand unloading position (as seen in FIG. 1), against the pressure of spring S, under the control of pressures exerted at the poppet valve 26, as described below. When so moved, pump 19 is unloaded, since the flow therefrom passes to suction through a connection 28 and a conduit C which leads to fluid reservoir 17. Such unloading movement of valve 25 takes place under control of the poppet valve 26. The shift, or unloading, point is determined by whether or not the poppet valve 26 is seated. Seating of the valve is, in turn, determined by the force of spring 29 and by other factors, including the pressure existing in circuit 11 and cross-over connection 27a.

While the unloading operation, and the action of the poppet valve 26 is shifting the unloading valve 25, will be discussed in detail with reference to FIGS. 2-4, further brief reference to the schematic showings of F 1G. 1. will facilitate an understanding of the more detailed description. Pressure in the line 16 of circuit 111 is sensed at one area of the poppet valve 26, via a conduit A which includes a restrictor 59, presently to be described. When the pressure sensed at the poppet valve 26 through the conduit A, plus the cross-over pressure communicated to the poppet valve through line 27a, (see the two parallel arrows in valve 26) exceeds the force of spring 29, the poppet valve moves from the lower, seated position shown, that is from the position in which the pump 19 is not bypassed, to an unseated position. As explained below, the unloading sequence is a function of the relative areas of the two poppet valve portions which are subject to the pressures in conduit A and line 27a, as well as the force exerted by the spring 29.

In the schematic showing of FIG. 1, the unseated position is an unillustrated upper position of the poppet valve in which it establishes a cross-passage through the poppet valve to the suction side of the pumps, through a portion of the conduit C. This cross-passage is designated B in the schematic showings of FIG. 1. Such upward, unseating, movement of the poppet valve 26 limits the force which was formerly assisting the spring S of control valve 25, to hold the spindle of said valve in its lefthand position. As a consequence, any further increase of the pressure communicated from line 16 (through the short conduit terminating in arrow R) results in a net force which moves the valve against the pressure of spring S and provides pressure relief by establishing a circuit through the unloading passage shown at 28. As will now be understood, when the valve 25 of circuit 10 has been moved to the right, the pump 19 is unloaded.

Now making more detailed reference to the construction of the control and poppet valves, and referring to FIGS. 2 and 3, it will be seen that the control valve 25 (and of course the similar valve 25a of circuit 11) is provided with a pair of inlet chambers 30 and 31 connected, respectively, to pumps 18 and 19 by passages 32 and 33. An outlet chamber 34 communicates with the bypass line 28 to return fluid to suction when the pump 19 is unloaded. The unloading movement of the valve 25 is under control of the pilot poppet valve 26.

The valve 25 is provided with a central bore containing a spool 35 mounted for shiftable movements within the bore between a first or lefthand position shown in FIG. 2, in which unloading of pump 19 occurs, and a righthand position in which the flow to pressure line 16 of circuit is the composite flow derived from both the pumps 18 and 19. Spool 35 is provided with a plurality of lands 36, 37 and 38 and with a bore 39 which is shown in dotted lines in FIGS. 2 and 3 and extends longitudinally throughout the major portion of the length of the spool 35. The lands 36, 37 and 38 confine the fluid within chambers formed by the central bore of the valve body and by side walls of the lands, and channel it through the various passageways. Orifices are provided through the wall of spool 35. One of these is shown at 40, and it comprises an inlet passage extending transverse the longitudinal axis of the spool and communicating with the bore 39 thereof. An outlet orifice shown at 41, is also bored radially inwardly through the wall of the spool. The described arrangement provides for flow of fluid from inlet chamber 30 to an outlet discharge chamber 42 which leads to pressure line 16 of circuit 10, the flow being via chamber 30, inlet orifice 40, spool bore 39, outlet orifice 41, and discharge chamber 42. Biasing means comprising the coil spring S urges the spool 35 to the righthand position shown in FIG. 3, (lefthand in schematic FIG. 1) in which both pumps are in circuit. A cap 43 retains the spring S in position in which it bears against the spool through land 36, said cap also preventing external leakage.

Flow from pump 18, through conduit 32, always en ters inlet chamber 30, which lies between lands 36 and 37 in either position of the spool, and hence always reaches discharge chamber 42 in the manner described above. When the spool occupies the righthand position shown in FIG. 3, the flow derived from pump 19, which enters the inlet chamber 31 as described above, passes through holes 44 provided in land 38 and thence traverses the ring type check valve 22 which is readily moved off its seat and against the stop 45, since essentially the same pressure exists in both of chambers 31 and 42. Under this condition, the flow from pump 19 also reaches chamber 42, via holes 44, and is discharged to the pressure line 16 of the associated load, as described. The check valve 22 is mounted for axial movement on the spool 35 and is movable back to a position in which it closes the openings 44 (FIG. 2), to prevent fluid flow from discharge 42 back to inlet port 31.

When the spool 35 of valve 25 shifts to the unloading position, that is to the lefthand position illustrated in FIG. 2, pump 19 is unloaded, since its output, derived from inlet chamber 31, flows laterally through a passage 31a, which has been uncovered by lefthand movement of land 37, and via which passage it flows to the bypass or discharge chamber 34 from whence it flows back to suction through conduit 28.

As explained above, and with reference to the embodiment herein described, if the input horsepower required to drive the pumps of both circuits tends to exceed the maximum available horsepower, as indicated by the sum of pressures at 16 and 16a (FIG. 1), then the spool of valve 25 is moved, in the manner described below, against the force of spring S, to the lefthand position shown in FIG. 2, in which the flow from pump 19 is bypassed. This is the condition which obtains when the poppet 46 of valve 26 is unseated. It is illustrated in FIG. 2, and results from such unseating of the pop- 6t. p The valve device 26 is responsive to pressure above a predetermined limit. As described with reference to FIG. 1, it is in communication with the pressure existing in circuit 10, via line 16 (this being the circuit under primary considerations for purposes of this description), as well as the pressure which is communicated from circuit 11 through cross-over connection 270. The shift, or unloading, point is determined by whether or not the poppet 46 of pilot valve 26 is seated. The relief pressure which will displace the valve from its seat 47 is, in turn, determined by the force of its spring 29 and by pressures in the two circuits, which pressures are brought to bear against particular areas of the poppet device, as described below.

As shown in FIG. 4, the poppet valve per se comprises a hollow spindle 48 terminating in a conical surface 49 which is the surface which engages the seat 47. The opposite end of the poppet 46 is stepped radially outwardly, as appears at 59, to provide an annular surface 51 against which pressure existing in cross-over connection 27a is brought to bear. As is apparent from FIGS. 2 and 3, cross-over connection 27a terminates at an inlet port 52 formed in the housing of the pilot valve 26. Spring 29 urges the poppet device toward its lefthand or seated position (FIG. 3), from whence it can be unseated by pressures exerted against surface 51 as well as against tapered surface 49. As seen below, unseating of the valve is a function of the force of spring 29 and of the ratio between the areas 49 and 51, against which are exerted the pressures existing in the two circuits. The pressure at surface 49 is communicated through an aperture 54 formed in the valve seat and which aperture is, in turn, in communication with the pressure existing in chamber 55.. The latter chamber is closed by a plug and nipple 56 to which is connected a line L, leading to a manually controllable dumping device D. Opening of the device D unloads the pumps through chamber 55 and line L. The resultant control by dumping fluid is particularly useful when the bucket (not shown) is used to position objects, for example pipes, in an excavation. Under such usage, control by dumping is often superior to reducing engine speed.

Chamber 55 communicates with chamber 57 of control valve 25 through a passage 58. Chamber 57 is also in communication with chamber 39, through a restricted aperture 59. In the described arrangement the conical surface 49 of the poppet device 46 is subject to pressure which is a function of that existing in chamber 39 of the control valve which, as described, is communicated to the pilot valve through the restriction 59, passage 58, and chamber 55 of the pilot valve assembly. In brief, whenever the poppet device 46 is seated, i.e., when both of pumps 18 and 19 are in pumping circuit, the poppet is subject to the pressure existing in line 16 of system 10 (via spool bore 39 and chambers 42 and 30) and said pressure is exerted against the conical face 49 of the valve. It is also subject to the crossover pressure exerted against the stepped surface 51. The sum of the forces created by these two pressures is, of course, in opposition to that exerted by the spring 29. In the embodiment presently described, the area of the surface 49, which is subject: to the pressure in chamber 30 (circuit 10 discharge pressure), and the area 51 which is directly subject to the cross-over pressure in circuit 11, are so chosen, as is the force of spring 29, that pump 19 of circuit 11) is unloaded when the pressure in circuit 11 exceeds a predetermined limit. There is essentially no pressure in the spring cavity because it is vented via a central bore 46, slots x (see particularly FIG. 4) and passage 60 to which further reference is made below.

It will now be appreciated that the pressure created at pump 18 is always communicated with the line 16 of circuit 10, via the cross-passage 4%, central bore 39 and cross-passage 41 of the spindle of control valve 25. During low pressure operation of the valve 25, it occupies its righthand position (FIG. 3) and pump 19 also delivers fluid to the line 16, as already described.

Since, as stated above, the pressure in chamber 30 of valve 25 is always the same as the pressure in chamber 42 thereof, in view of the communication through the valve spool, and it will therefore be observed that the pressure existing in chamber 55, just ahead of poppet 46, is also a function of the discharge pressure of the valve 25, via restrictor 59 and the generally radial passage 58, which places the valve 25 in communication with the chamber 55. During low pressure operation the pressures in chambers 57 and 42 are equal. The force of spring S then maintains the spool 35 at the righthand end of its bore (FIG. 3).

In summary, the cross-over unloading arrangement of the invention, as thus far described, includes such a ratio between areas 49 and 51 that, if the piston in one circuit encounters a high load condition, the resultant elevated pressure in said one circuit unloads one of the pumps in the other circuit, leaving more power available for the piston circuit which has encountered high load. Should a high load condition then develop in said other circuit, there will be unloading of one of the pumps in said one circuit, with the result that the power available at the prime mover is divided between only two pumps. The action of the described embodiment can be summarized as follows, it being assumed that the initial overpressure develops in circuit 11.

The pressure acting on the lefthand side of the spool 35 of valve 25 in circuit 10, that is the pressure existing in chamber 57, is exerted against the tapered face 49 of the pilot poppet valve 26 because of the presence of the passageway 58. This pressure, plus the pressure communicated from circuit 11 (through conduit 27a) acting on the area at the annular face 51 of stepped spindle 48, will, at a particular relief value determined in advance, produce a force that exceeds the force exerted by spring 29, and hence unseat the poppet valve. Such movement of the poppet valve to the righthand position shown in FIG. 2 opens up the passageway through the valve seat 47, and thence through the diagonal passageway 60 in the body of valve 25, to a groove 61 which is in communication with discharge chamber 34 which leads to discharge line 28. The result is that the pressure on the lefthand side of the spool 35 is not allowed to exceed the particular relief value. A further increase in pressure in circuit or 11 acts to force the spool 35 to its lefthand position (FIG. 2) and the pump 19 is unloaded to suction, all as considered above with reference to the schematic showings of FIG. 1.

Should the pressure in circuit 10 continue to exceed the limit, after initial unloading, the cross-over connection 27 which leads to circuit 11, and the control and pilot valves a and 26a of circuit 11 provide relief by unloading pump 19a of the latter circuit. As noted above, should either P or P rise to a maximum value above the relief limit, the safety unloader of the affected circuit (e.g., the unloader 23 of circuit 10) will operate to bypass to reservoir both pumps of such affected circuit.

While the system as thus far described results in unloading of a pump at lower pressure, in a first circuit, in response to a piston, in a second circuit, encountering a load which increases the pressure, in the second circuit, above a predetermined relief value, it should be understood that the system may be preset to produce unloading in any one of four specific priority sequences. These different unloading sequences are:

I. The unloadable pump subject to the lower pressure in its individual circuit unloads first, as is the case in the embodiment described above;

2. The unloadable pump subject to the higher pressure in its individual circuit unloads first;

3. The unloadable pump in circuit 10 unloads first, regardless of which circuit is encountering the overload;

4. The unloadable pump in circuit Ill unloads first, regardless of which circuit is encountering the overload.

These different sequences, and the relief values at which they occur, are achieved by proper selection of the force of springs 29, 29a, and by suitable control of the size of, and ratios between, the areas 49 and 51 of the poppet devices. Such selection of spring constants, and of ratios between the poppet-actuating areas, in the valve assemblies of the two circuits, is all that is required to provide relief at the desired settings and in the selected sequence. Specifically, selection of the ratio of areas determines whether operation under sequence 1 or 2 is achieved, and selection of the force of the poppet spring in one valve assembly, relative to the force of the poppet spring in the other assembly, determines whether unloading is in accordance with sequence 3 or 4.

I claim;

1. In an hydraulic control system of the kind including a pair of hydraulic circuits each having a pair of fluid supply pumps to be driven by a prime mover common to both circuits, each having an actuator to be driven in either of two senses in accordance with the flow of fluid in the circuit, and each circuit further including means for controlling the flow of fluid to the actuator of that circuit, the improvements which comprise: means in each circuit movable to unload one pump of that circuit; and means for effecting such movement of the movable means in response to fluid pressure in the other circuit increasing above a predetermined value.

2. A system in accordance with claim I, and further characterized in that said movable means comprises pressure-responsive valve means, and said last means comprises fluid flow conduit means cross-connecting the pressure-responsive valve means of each circuit with the other circuit.

3. A system in accordance with claim 2, and in which the valve means in each circuit includes, a part shiftable in response to a predetermined pressure difference thereacross to effect such unloading, and a pilot valve so disposed in circuit with said conduit means so as to subject said part to such pressure difference when the pressure in the other circuit increases above said predetermined value.

4. A system in accordance with claim 3, and in which said pilot valve includes a poppet member subject to a force which biases it toward a closed position in which it doeos not subject said part to such difference, said poppet member being so connected in the system as to be subject to two forces which oppose its bias, one such force being a function of a pressure prevailing at one side of said shiftable part, and the other such force being a function of the pressure existing in the other circuit and communicated through said conduit means.

5. A system in accordance with claim 2, and in which said valve means comprises: a spool type control valve responsive to a predetermined imbalance of pressures thereacross to move to unloading position; and a poppet type pilot valve in communication with said spool valve and said conduit means and which, when unseated, subjects said spool valve to such imbalance of pressures, said poppet valve being so constructed and connected in the system that it is unseated when the pressure in said other circuit increases above said predetermined value.

6. A system in accordance with claim 1, and further characterized in that: said movable unloading means comprises a control valve responsive to pressures existing thereat to shift to an unloading position; and said last means comprises a pilot valve for causing such shifting of said control valve, said pilot valve having a portion connected in fluid flow relation with said control valve, to vary the pressure thereat, and a portion subject to the pressure prevailing in said other circuit, the construction and arrangement being such that an increase in the pressure prevailing in said other circuit above said predetermined value so actuates said pilot valve as to cause shifting of said control valve to its unloading position.

'7. In a hydraulic control system of the type including a pair of hydraulic circuits, each having a cylinder and a piston, and pump means to be driven by a prime mover common to both circuits, the pump means of at least one circuit comprising two pumps: fluid flow control means in each circuit for directing fluid from the pump means to the circuit cylinder for actuating its piston in either of two senses, in accordance with the flow of fluid to said cylinder; and means for unloading one pump of said one circuit, said latter means being responsive to the fluid pressure in either circuit increasing above a predetermined limit.

8. in a system in accordance with claim 7, the further characterization that said last recited means comprises pressure-responsive valve means in said one circuit movable to an unloading position, and conduit means for subjecting said valve means to the pressure prevailing in both circuits.

9. In a system in accordance with claim 8, the further feature that said other circuit is also provided with pressure-responsive valve means movable to an unloading position, and in which system there is provided additional conduit means for subjecting the latter valve means to the pressures prevailing in both circuits.

10. In a fluid control system, a pair of hydraulic circuits each having: a pair of fixed displacement pumps with supply and discharge passages for supplying operating fluid from a reservoir to a load; control valve means including a movable valve member and valve passages for delivering the fluid discharged from the pumps to the load, said valve member being movable to a first position to combine the flow of fluid from said pumps for delivery from the load and to a second position in which the flow of fluid from one only of said pumps is delivered; and means for actuating said valve means, said latter means in each circuit being coupled to the other circuit and responsive to pressures prevailing in both circuits, including attainment of a predetermined limit of pressure in the other circuit, for moving the valve member to its second position,

it. A fluid control system according to claim 110, wherein the valve actuating means comprises a second valve member connected in fluid flow communication with the output of one of said pumps of one of said circuits, said second valve member including a shiftable poppet device operable, in response to a predetermined limit of pressure in said other circuit, to move said first valve member to its second position.

12. For use in a fluid flow control system having a pair of fixed displacement pumps, each having supply and discharge passages for the supply and discharge of operating fluid from a reservoir, control valve means comprising: a valve housing including first and second inlet passages each adapted for connection to the discharge passage of a corresponding one of such pumps; first and second valve outlet passages, said first passage being connectible to a load forming part of such a circuit, said second outlet passage being adapted for communication with a pump suction passage, said control valve means further including; a spool member mounted for movement within said housing and operative in one position to connect said first and second valve inlet passages to said first valve outlet passage, and in another position to connect one valve inlet passage to said second outlet passage; and means adapted for connection to an associated hydraulic circuit and effective to exert pressure against the spool member to move it to its second position when the pressure in said associated hydraulic circuit reaches a predetermined value.

13. Valve means in accordance with claim 12, and in which said last means comprises, a poppet valve biased toward a closed position in which said spindle remains in its first position, and means for subjecting said poppet valve to a force which is a function of the pressure existing in such an associated circiuit, such force, when the pressure exceeds a predetermined value, moving said poppet to open position in which it causes movement of said spindle to its second position.

14. Valve structure for use in unloading a pump of a first hydraulic actuating circuit in response to pressure prevailing in a second hydraulic actuating circuit, said structure comprising: control valve means responsive to pressure existing thereat to shift to a position in which it unloads such pump; and pilot valve means for causing such shifting of said control valve means, said pilot valve means having a portion coupled in fluid flow relation with said control valve means to vary the pressure at the latter in response to pressure conditions existing at said pilot valve means, and also having a port adapted for open connection to such a second hydraulic circuit, the construction and arrangement being such that an increase in the sum of the pressures prevailing at said pilot valve means and in said port, above a predetermined value, so actuates said pilot valve means as to cause shifting of the valve means to its unloading position.

15. Valve structure in accordance with claim 14, and in which said control valve means comprises a spool shiftable along its longitudinal axis to unload a pump of such a first hydraulic circuit, the coupling between said pilot valve means and said control valve means placing one end of said spool in communication with a pressure existing at said pilot valve means, and in which structure said pilot valve means comprises a poppet member unseating of which results in varying the pressure at said one end of said spool and consequent shifting of said spool to its unloading position, said pilot valve member having surface area subject to the pressure existing at said port and against which surface area there is created a force which unseats said poppet member when the pressure in such a second associated circuit exceeds a predetermined value.

16. Valve structure for use in unloading a pump of an associated hydraulic actuating circuit in response to pressures prevailing in another associated hydraulic actuating circuit, said structure comprising: a spool member shiftable, in response to a predetermined pressure difference existing thereacross, to move to a position in which it unloads such pump; a pilot valve; first conduit means interconnecting a chamber in said pilot valve with one side of said spool member; second conduit means through which the pressure prevailing in another associated circuit may be brought to bear against a surface of said pilot valve, predetermined increases in pressure, in said first and second conduit means, serving to move said pilot valve to a position in which it increases the difference of pressure across said spool and causes said spool to shift to its unloading position.

17. A hydraulic fluid system comprising a pair of hydraulic circuits each having a fluid pressure load, and each having pump means for supplying pressurized op erating fluid, the pump means for a first of said pair of circuits comprising two pumps, controllable means for delivering the combined flow of fluid from both of said pumps to the load of said first circuit and for alternatively delivering the flow of fluid from only one of said pumps to the load of said first circuit, and means for actuating said controllable means including means operative by fluctuation of pressure above and below a predetermined pressure value in the second circuit, the sense of such actuation being to deliver fluid from only one pump when the pressure in the second circuit rises above said predetermined value and to deliver the combined flow of both pumps when the pressure in the second circuit falls below said predetermined value.

5 ,ees,a21 March 4, 1935 Patent No Dated lnventofls) Frank Ratliff and James R. MeB'ur'nett It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the title page, in the address of the assignee:

"Mass." should be -Miss Column 3, Line 64 (Page 7, Line 18) "prpessure" should be -'pressure-.

Column 5, Line 44 (Page 10, Last Line) Insert -chamber-- after discharge.

Column 6, Line 3 (Page 11, Line 20 and 21) Change "considerations" to -consideration-.

Column 7 Line 6 (Page 13 Line 25) Change "spindle to --spool.

Column 9 Line 64 (Claim 10, Line 8) Change "from" to --to- Column 10, Line 36 (Claim 13, Line 3) Change "spindle" to -spool-.

Column 10, Line 42 (Claim 13, Line 13) Change "spindle" to -spool--.

Signed and sealed this 1st day of July 1975.

C. RSHALL DANN- RUTZ'; C. IEASON Commissioner of Patents Attesting Officer and Trademarks 

1. In an hydraulic control system of the kind including a pair of hydraulic circuits each having a pair of fluid supply pumps to be driven by a prime mover common to both circuits, each having an actuator to be driven in either of two senses in accordance with the flow of fluid in the circuit, and each circuit further including means for controlling the flow of fluid to the actuator of that circuit, the improvements which comprise: means in each circuit movable to unload one pump of that circuit; and means for effecting such movement of the movable means in response to fluId pressure in the other circuit increasing above a predetermined value.
 2. A system in accordance with claim 1, and further characterized in that said movable means comprises pressure-responsive valve means, and said last means comprises fluid flow conduit means cross-connecting the pressure-responsive valve means of each circuit with the other circuit.
 3. A system in accordance with claim 2, and in which the valve means in each circuit includes, a part shiftable in response to a predetermined pressure difference thereacross to effect such unloading, and a pilot valve so disposed in circuit with said conduit means so as to subject said part to such pressure difference when the pressure in the other circuit increases above said predetermined value.
 4. A system in accordance with claim 3, and in which said pilot valve includes a poppet member subject to a force which biases it toward a closed position in which it doeos not subject said part to such difference, said poppet member being so connected in the system as to be subject to two forces which oppose its bias, one such force being a function of a pressure prevailing at one side of said shiftable part, and the other such force being a function of the pressure existing in the other circuit and communicated through said conduit means.
 5. A system in accordance with claim 2, and in which said valve means comprises: a spool type control valve responsive to a predetermined imbalance of pressures thereacross to move to unloading position; and a poppet type pilot valve in communication with said spool valve and said conduit means and which, when unseated, subjects said spool valve to such imbalance of pressures, said poppet valve being so constructed and connected in the system that it is unseated when the pressure in said other circuit increases above said predetermined value.
 6. A system in accordance with claim 1, and further characterized in that: said movable unloading means comprises a control valve responsive to pressures existing thereat to shift to an unloading position; and said last means comprises a pilot valve for causing such shifting of said control valve, said pilot valve having a portion connected in fluid flow relation with said control valve, to vary the pressure thereat, and a portion subject to the pressure prevailing in said other circuit, the construction and arrangement being such that an increase in the pressure prevailing in said other circuit above said predetermined value so actuates said pilot valve as to cause shifting of said control valve to its unloading position.
 7. In a hydraulic control system of the type including a pair of hydraulic circuits, each having a cylinder and a piston, and pump means to be driven by a prime mover common to both circuits, the pump means of at least one circuit comprising two pumps: fluid flow control means in each circuit for directing fluid from the pump means to the circuit cylinder for actuating its piston in either of two senses, in accordance with the flow of fluid to said cylinder; and means for unloading one pump of said one circuit, said latter means being responsive to the fluid pressure in either circuit increasing above a predetermined limit.
 8. In a system in accordance with claim 7, the further characterization that said last recited means comprises pressure-responsive valve means in said one circuit movable to an unloading position, and conduit means for subjecting said valve means to the pressure prevailing in both circuits.
 9. In a system in accordance with claim 8, the further feature that said other circuit is also provided with pressure-responsive valve means movable to an unloading position, and in which system there is provided additional conduit means for subjecting the latter valve means to the pressures prevailing in both circuits.
 10. In a fluid control system, a pair of hydraulic circuits each having: a pair of fixed displacement pumps with supply and discharge passages for supplying operating fluid from a reservoir to a Load; control valve means including a movable valve member and valve passages for delivering the fluid discharged from the pumps to the load, said valve member being movable to a first position to combine the flow of fluid from said pumps for delivery from the load and to a second position in which the flow of fluid from one only of said pumps is delivered; and means for actuating said valve means, said latter means in each circuit being coupled to the other circuit and responsive to pressures prevailing in both circuits, including attainment of a predetermined limit of pressure in the other circuit, for moving the valve member to its second position.
 11. A fluid control system according to claim 10, wherein the valve actuating means comprises a second valve member connected in fluid flow communication with the output of one of said pumps of one of said circuits, said second valve member including a shiftable poppet device operable, in response to a predetermined limit of pressure in said other circuit, to move said first valve member to its second position.
 12. For use in a fluid flow control system having a pair of fixed displacement pumps, each having supply and discharge passages for the supply and discharge of operating fluid from a reservoir, control valve means comprising: a valve housing including first and second inlet passages each adapted for connection to the discharge passage of a corresponding one of such pumps; first and second valve outlet passages, said first passage being connectible to a load forming part of such a circuit, said second outlet passage being adapted for communication with a pump suction passage, said control valve means further including a spool member mounted for movement within said housing and operative in one position to connect said first and second valve inlet passages to said first valve outlet passage, and in another position to connect one valve inlet passage to said second outlet passage; and means adapted for connection to an associated hydraulic circuit and effective to exert pressure against the spool member to move it to its second position when the pressure in said associated hydraulic circuit reaches a predetermined value.
 13. Valve means in accordance with claim 12, and in which said last means comprises, a poppet valve biased toward a closed position in which said spindle remains in its first position, and means for subjecting said poppet valve to a force which is a function of the pressure existing in such an associated circuit, such force, when the pressure exceeds a predetermined value, moving said poppet to open position in which it causes movement of said spindle to its second position.
 14. Valve structure for use in unloading a pump of a first hydraulic actuating circuit in response to pressure prevailing in a second hydraulic actuating circuit, said structure comprising: control valve means responsive to pressure existing thereat to shift to a position in which it unloads such pump; and pilot valve means for causing such shifting of said control valve means, said pilot valve means having a portion coupled in fluid flow relation with said control valve means to vary the pressure at the latter in response to pressure conditions existing at said pilot valve means, and also having a port adapted for open connection to such a second hydraulic circuit, the construction and arrangement being such that an increase in the sum of the pressures prevailing at said pilot valve means and in said port, above a predetermined value, so actuates said pilot valve means as to cause shifting of the valve means to its unloading position.
 15. Valve structure in accordance with claim 14, and in which said control valve means comprises a spool shiftable along its longitudinal axis to unload a pump of such a first hydraulic circuit, the coupling between said pilot valve means and said control valve means placing one end of said spool in communication with a pressure existing at said pilot valve means, and in which structure saiD pilot valve means comprises a poppet member unseating of which results in varying the pressure at said one end of said spool and consequent shifting of said spool to its unloading position, said pilot valve member having surface area subject to the pressure existing at said port and against which surface area there is created a force which unseats said poppet member when the pressure in such a second associated circuit exceeds a predetermined value.
 16. Valve structure for use in unloading a pump of an associated hydraulic actuating circuit in response to pressures prevailing in another associated hydraulic actuating circuit, said structure comprising: a spool member shiftable, in response to a predetermined pressure difference existing thereacross, to move to a position in which it unloads such pump; a pilot valve; first conduit means interconnecting a chamber in said pilot valve with one side of said spool member; second conduit means through which the pressure prevailing in another associated circuit may be brought to bear against a surface of said pilot valve, predetermined increases in pressure, in said first and second conduit means, serving to move said pilot valve to a position in which it increases the difference of pressure across said spool and causes said spool to shift to its unloading position.
 17. A hydraulic fluid system comprising a pair of hydraulic circuits each having a fluid pressure load, and each having pump means for supplying pressurized operating fluid, the pump means for a first of said pair of circuits comprising two pumps, controllable means for delivering the combined flow of fluid from both of said pumps to the load of said first circuit and for alternatively delivering the flow of fluid from only one of said pumps to the load of said first circuit, and means for actuating said controllable means including means operative by fluctuation of pressure above and below a predetermined pressure value in the second circuit, the sense of such actuation being to deliver fluid from only one pump when the pressure in the second circuit rises above said predetermined value and to deliver the combined flow of both pumps when the pressure in the second circuit falls below said predetermined value. 